The present invention relates to a method in a treatment process of a paper web wherein in the treatment process, the paper web travels via a surface journaled rotatable, such as the peripheral surface of a cylinder or roll and the treatment process is controlled with an adjustment and control unit. The present invention also relates to a treatment device for carrying out this method.
In particular, the invention relates to such a treatment processes in which a web travels a long distance via a surface journalled rotatable or only in a short nip contact thereto, and the web is subjected to a force affecting the web in the form of a nip pressure and/or tension. An example of the treatment process of the paper web is the reeling process of a continuous reel-up. In the reeling process, a continuous web of several meters in width, passed from the previous sections of a paper machine or finishing apparatus for paper, is reeled around a reel core (reel spool). The web is passed onto the reel via a reeling cylinder, wherein a particular linear pressure prevails in the reeling nip between the reeling cylinder and the reel (the point where the web is passed on the reel guided by the reeling cylinder), the linear pressure being produced with suitable loading arrangements, by means of which a particular loading force is attained between the reeling cylinder and the reel. This is typically implemented by loading the reel with force devices connected to the ends of the reel core on both edges of the reel.
The control of the loading is crucial in the reeling process, because the used loading affects the quality of the reel and its behaviour in the further processing. It should be possible to accurately measure the linear pressure effective in the reeling nip, and the actuators affecting the linear pressure should be controlled by means of the same. The control and management of the linear pressure or xe2x80x9cnip forcexe2x80x9d is, however, difficult primarily because of the point of action of the force to be measured (the contact point between the reeling cylinder rotating at high peripheral speed and the reel). The reeling can also be effected at different angles with respect to the reeling cylinder, i.e. the location of the nip on the periphery of the reeling cylinder can vary, especially during so-called initial reeling. This complicates the act of calculating the linear pressure solely on the basis of the loading by the force device, because the mass of the reel, which is constantly growing, as well as the location of the reel, affect the linear pressure.
Heretofore, force sensors have been used in the structures of the reel-up to measure the linear pressure, and as examples of these principles, it is possible to mention the publications WO 97/22543, U.S. Pat. No. 5,611,500 and EP 517830. By means of measurement signals given by the sensors, it is possible to adjust the reeling operation. In order to obtain sufficient information on the actual linear pressure, i.e, nip force at different stages of the reeling, sensors have to be placed in several different locations. Several separate components cause interference factors, and their properties change in different ways during time, wherein it is difficult to control the changes. Similarly, it has been observed in practice that the force sensors are liable to break in a paper machine environment. The force sensors also have to be dimensioned to oversize because of possible high force peaks which are always produced during the reeling. Part of the sensors have to be placed in movable parts, wherein lines are necessary for conducting signals therefrom to the control system. Since the measurement in question is an indirect measurement, different friction factors cannot be eliminated.
Another treatment process for the paper web in which an accurate control of the linear pressure has to be attained, is calendering. The calendering process is disclosed e.g. in the Finnish patent 96334 and in the corresponding U.S. Pat. No. 5,438,920.
The purpose of the invention is to present a solution for the aforementioned problems and a new method in the reeling process of a paper web, as well as a reel-up for a paper web, by means of which the linear pressure can be controlled more accurately. To attain this purpose, the method according to the invention is primarily characterized in what will be presented in the characterizing part of the appended claim 1. The device according to the invention, in turn, is characterized in what will be presented in the characterizing part of the appended claim 11.
The invention is based on the idea that the bearing arrangement used for the moving surface which guides the web and with which, for example in the case of a reel-up, the reel to be formed from the web is in contact, is a bearing, which is of such a type that it requires external energy, control energy, to maintain its operation, i.e. the clearance of the bearing that enables rotation requires a certain power. The signal obtained from the control energy of the bearing is utilized in the control of the treatment process. In the reel-up and in the calender, the signal is used especially to control the linear pressure, i.e. the nip force.
The entire linear pressure, i.e. the nip force, acts on the moving surface in question, which typically is a cylinder or a roll journalled rotatable in the frame of a part of the machine. This force is also manifested in the function of the bearing which requires energy. Thus, the bearing can be used in the reel-up to determine all nip forces, irrespective of the position or the mass of the reel, i.e. both during the initial reeling, wherein the reel can be located more or less above the horizontal plane extending via the central axle of the reeling cylinder, as well as in the final reeling in the actual reeling station in which the reel grows into its full size. There is only one measurement point, or if the bearing arrangements of both sides are utilized, there are two measurement points at the most, and the interferences occurring therein can be more easily controlled.
In the calender, the bearing can be used in the bearing arrangement of one or more calender rolls, wherein the loading exerted on the roll can be measured and the calendering process, especially the loading devices determining the linear pressure affecting the paper passed through the calender nip, can be controlled by means of the same.
A third advantageous target of use is a roll guiding the paper web, over which roll the web travels with a particular tension. Thus, the tension causes a certain force to the roll in the radial direction, which force can be detected from the signal obtained from the control energy of the bearing arrangement of the roll. On the basis of this information it is possible to control the draw difference.
According to a preferred embodiment, it is possible to use a magnetic bearing. In the magnetic bearing it is possible to maintain the clearance by adjusting the electric current to be supplied to the bearing. The force acting upon the reeling cylinder, the calender roll or the roll for measuring tension also has effect on this need for electric current, and on the basis of this it is possible on the basis of the magnitude of the electric current supplied or the magnitude of a variable proportional thereto, to obtain information on the forces acting on the cylinder or the roll journalled by means of the magnetic bearing, such as the nip load acting on the reeling cylinder, the loading effected by the calender nip to the calender roll, or the force applied to the roll by the tension of the web guided by a guide roll.
By virtue of the invention, it is not necessary to estimate the effect of the frictions of different movable parts in the control. The measurement takes place with the minimum of one member (a bearing arrangement requiring control energy), which provides a result in which different friction factors have been eliminated.